Electronic power regulation control device for providing constant electrical power to a load of varying impedance

ABSTRACT

An electronic power regulation control device for providing constant electric power to a load of varying impedance. The device may be operated to provide degenerative or regenerative regulation with varying load peaks. The device does not require feedback but under certain conditions feedback may enhance the performance. The basic power regulating device is a thermionic electron device wherein the voltage-current characteristic approximates the ideal hyperbolic curve of constant power. This is accomplished by combining the characteristics of a current limiting, temperature limited thermionic diode in conjunction with that of a thermionic triode in a parallel combination. It is also possible to combine the functions of a control diode of high perveance and a control diode of low perveance to also approach a characteristic curve of constant power.

United States Patent Hruda 1 51 Aug. 29, 1972 [54] ELECTRONIC POWERREGULATION CONTROL DEVICE FOR PROVIDING CONSTANT ELECTRICAL POWER TO ALOAD OF VARYING IMPEDANCE [72] Inventor: Robert M. Hruda, Horseheads,N.Y.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: Jan.26, 1971 21 Appl.No.: 109,847

783,360 4/1935 France ..328/249 Primary Examiner-John W. HuckertAssistant Examiner-Andrew J. James Att0rneyF. l-l. Henson and C. F. Renz[57] ABSTRACT An electronic power regulation control device forproviding constant electric power to a load of varying impedance. Thedevice may be operated to provide degenerative or regenerativeregulation with varying load peaks. The device does not require feedbackbut under certain conditions feedback may enhance the performance. Thebasic power regulating device is a thermionic electron device whereinthe voltage-current characteristic approximates the ideal hyperboliccurve of constant power. This is accomplished by combining thecharacteristics of a current limiting, temperature limited thermionicdiode in conjunction with that of a thermionic triode in a parallelcombination. It is also possible to combine the functions of a controldiode of high perveance and a control diode of low perveance to alsoapproach a characteristic curve of constant power.

7 Claims, 8 Drawing Figures D.C. POWER SUPPLY SUPPLY Patented Aug. 29,1972 3,688,204

2 Sheets-Sheet 2 18 22 16 D.C. 44 POWER Y SUPPLY ---P mm A c We POWERPOWER A5 SUPPLY SUPPLY FIG. 5.

HIGH M' 72 PERVEANCE REGION LOW ANODE PERVEANCE REGION FIG. 6. FIG. 8. 4

PARALLEL COMBINATION 80 82 HIGH PERVEAMCE DIODE LOW PERVEANCE DIODE FIG.7

ELECTRONIC POWER REGULATION CONTROL DEVICE FOR PROVIDING CONSTANTELECTRICAL POWER TO A LOAD OF VARYING IMPEDANCE BACKGROUND OF THEINVENTION There are many control devices in industry utilized forcontrolling electric power. Most of these devices are directed toproviding either a constant voltage or a constant current and are notdirected to the problem of providing a regulation system that providesconstant power across a varying load.

One typical application is that in dielectric heating. In such a heatingsystem, a power supply converts AC power into DC power and delivers itto an oscillator. The oscillator generates radio frequency power thatgoes to the heating load. Normally, the power for such a system iscontrolled at the input side of the power supply. If the power level islow, a variable transformer might be used. If it is high, either aninduction regulator or saturable core reactor could be used. In all ofthese methods, the quantity being controlled is the amount of AC currentbeing rectified in the power supply.

Another system employs a power control diode in which the power supplyis designed to produce full output when it is turned on and is notvariable. The control diode is inserted between the power supply and theoscillator. The input to the diode filament controls its emission, whichin turn, determines the voltage drop between the filament and anode ofthe diode. Thus, the diode acts as a high power resistor between thepower supply and the load. Typically, a change of only four watts offilament power to the diode results in a load change of 1 kilowatt. Bycontrol of the current applied to the filament to provide a certainamount of emission current, the diode conducts essentially the same setcurrent no matter how much the load increases. It is also possible bysetting the diode to operate at the proper point past the knee of thecharacteristic curve to cause it to adjust its operation to suit avariety of load conditions. For example, in the drying of a foam rubbermattress by dielectric heating, the mattress contains a considerableamount of water when it first enters between the electrodes and thisprovides a heavy load on the dielectric heater. By the time the mattresscomes out, all the water is gone and so the load on the heater isrelatively light. If too much power is fed through the heater initially,rubber cells will be destroyed and steam will blow the mattress apart,yet, if the heater control is set unnecessarily low, the drying processtakes longer than is necessary and therefore would restrict productionrate. The problem is solved by setting the control diode so that thepower supply voltage is divided between the load and the diode. As themattress dries, the load line swings counterclockwise and the loadvoltage increases as a consequence. The diode voltage decreases. By thisprogressive delivery of more voltage to the load as the mattress dries,a more uniform power input to the mattress is provided and the mattressdries faster than could be safely done with other control methods.

Another example of a power control diode use is in RF heating of aplastic. The plastic starts as a good insulator but as heat goes intoit, it becomes more and more conductive and so the heat flows in fasterad faster. By using the control diode set at the knee of thecharacteristic curve, the voltage delivered to the RF generator isreduced as the plastic heats. The load line in this case will go in aclockwise direction.

SUMMARY OF THE INVENTION This invention is directed to a powerregulation device which provides constant electric power to a load whoseimpedance is varied. The device incorporates a current limiting functionof a temperature limited thermionic' diode in conjunction with a biasedtriode to approximate the ideal hyperbolic curve of constant power.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention, reference may be had to the preferred embodiments, exemplaryof the invention, shown in the accompanying drawings, in which:

FIG. 1 is a view of a power regulation device partly in sectionincorporating the teachings of this invention;

FIG. 2 illustrates a curve for a theoretical constant power regulation;

FIG. 3 illustrates curves of the properties of the device shown in FIG.1 to accomplish substantially a theoretical constant power control;

FIG. 4 is another illustration of the change in operatingcharacteristics of the device shown in FIG. 1 in response to appropriatecontrol potentials applied to the electrodes;

FIG. 5 is a schematic diagram of a circuit used in connection with thepower regulator device illustrated in FIG. 1;

FIG. 6 is a view illustrating a possible modification of the deviceshown in FIG. I and incorporating the teachings of this invention;

FIG. 7 is a set of curves illustrating the electrical properties of thedevice shown in FIG. 6; and

FIG. 8 illustrates another possible modification of the device shown inFIG. 1 incorporating the teachings of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there isshown a power control device consisting of an envelope 10 which isevacuated by means of an exhaust tubulation l4. Positioned within theenvelope 10 is a triode filament 16 which is in the form of a helicalwire of a suitable material such as tungsten. The filament 16 issupported by means of a pair of support leads 17 of a suitable materialsuch s molybdenum. Positioned about the triode filament 16 is a diodefilament 18. The diode filament 18 consists of a plurality of filamentstrands 19 which are in the shape of hairpins and are mutually joined atthe upper end and closed portion by a suitable molybdenum braze. Theends of the diode filament strands are welded to a pair of notched discs20 of a suitable material such as molybdenum. An anode 22 which is of asuitable material such as copper forms a part of the envelope 10. Ajacket 24 surrounds the anode 22 and provides means of circulating waterabout the outer surface of the anode 22. Inlet means 26 to the waterjacket 24 provides means for introducing a suitable liquid such as waterinto the water jacket 24 and outlet means 28 provides means of removingthe liquid from the water jacket 24. Terminals 30 are provided forapplying suitable currents to the filaments 16 and 18, and an exteriorcontact may be made directly to the exterior surface of the anode 22.

FIG. illustrates the electrical connection of the power device shown inFIG. 1 into a typical circuit. A suitable power supply 32 is providedfor providing direct current power. The positive terminal of the powersupply 32 is connected to the anode 22. Current supplied to the diodefilament 18 is provided by means of a suitable AC power supply 35connected through a filament transformer 34. Suitable current issupplied to the triode filament 16 by means of a suitable AC powersupply 37 connected through a filament transformer 36. The powersupplied to the transformers 34 and 36 is variable in nature so as toprovide desirable electrical characteristics of the power control devicethat will be explained later. A lead 38 is provided from the midpoint ofthe secondary of the transformer 36 which is connected to the cathodeterminal of a Zener diode 42 and a lead 40 is provided from the midpointterminal of the secondary of the transformer 34 to the anode terminal ofthe Zener diode 42. The anode of the Zener diode 42 is coupled to a load44 and the other side of the load 44 is connected to ground. The Zenerdiode 42 may be replaced by any form of voltage source such as a batteryor cathode resistor to provide a suitable bias between the filaments l6and 18.

Referring now to FIG. 2, a theoretical constant power curve isillustrated by the curve 50. If the load line 51 of the system as isillustrated in FIG. 2 is at point b, then the distribution of voltagebetween the power control device and the load is as indicated. In theevent that the load line 51 should vary in a counterclockwise directionso as to intersect the curve 50 at point a, then the voltage drop acrossthe power control device would be small while the voltage across theload would be large. In either case, the power across the load would beconstant. I

FIG. 3 illustrates the two functions of the power control device thatprovides an electrical characteristic illustrated as curve 52 in FIG. 3.The electrical characteristic curve 52 is obtained by combining theelectrical properties of the diode section consisting of the filament 18and the anode 22 to provide curve 54 and the electrical characteristicsof the triode section including the filament 16, the anode 22 and thegrid function of the filament 18 to provide the curve 56. The termcontrol diode as used herein is characterized by the curve 54 in FIG. 3.This curve 54 may be expressed mathematically as follows:

In the region extending from the origin to pointthe curve is termedspace charge limited, and obeys the classical 3/2 power law:

where I is anode current K is a constant determined by geometry V isanode voltage.

In the region extending fromCDto the right the curve 54 is termedtemperature limited," and obeys Dushman's and Schottky's equations:

1=1 exp (4.389 E /T) where I is again anode current I, is peak emissioncurrent E is the electrostatic field on the emitter T is temperature Aand b are physical constants determined by the emitter material Expdenotes epsilon raised to the indicated power. A description is found onp. 8-14 and 109-110 in Physics of Electron Tubes by Keller.

In FIG. 4 there is illustrated a typical electrical characteristic curve60 of a power control device. By increasing the negative bias betweenthe filaments l6 and 18, one is able to modify the electricalcharacteristics to the curve 62. This may be accomplished by providing avariable power supply in place of the Zener diode 42. In addition, byreducing the temperature of the filaments 18 one can modifysubstantially the characteristics of the tube so as to obtain a curvesimilar to curve 64 as illustrated in FIG. 4. In this manner, byproviding separate control of the temperature of the filaments l6 and 18and the application of bias therebetween, a wide range of controlledpower characteristics may be obtained from the power control device.

In FIG. 6 there is illustrated another possible modification to providea substantial constant power control characteristics in which a commonelongated filament is utilized and in which the anode 72 consists of asection 74 having a small diameter and a second section 76 having alarger diameter. In this manner the anode region associated with theanode 76 is a low perveance region while the anode region associatedwith the anode portion 74 is the high perveance region.

FIG. 7 illustrates the electrical characteristics obtained by such adevice in which the connection of the device in parallel combinationprovides the curve 80 while the high perveanc'e diode portion 74provides a curve 82 and the low perveance diode section provides thecurve 84.

In FIG. 8 another possible modification is illustrated which consists ofan anode of uniform diameter 90, a common emitter 92, and a grid member94 which extends only for a portion of the length of the anode and theemitter 92.

I claim as my invention:

1. A power control device comprising a first and second electricaldischarge means in which said first means operates in the temperaturelimited region of a diode electrical characteristic and said secondmeans operates in a triode electrical characteristic and terminal meansfor applying power through said power control device to a load, saidfirst and second means of said device connected in electrical parallelto provide in combination an electrical characteristic correspond ing toa substantially uniform power control electrical characteristic withvarying loads.

2. The device of claim 1 in which said first means is an electricaldischarge control diode and said second means is an electrical dischargetriode.

6. The device as set forth in claim 1 in which said first means consistsof a first filament, said second means consists of a second filamentsurrounding said first filament with a bias provided between said firstand second filaments, and a common anode for said first and secondmeans.

7. The device set forth in claim 6 in which said means for applyingpower is connected to said anode and said load is connected to saidfirst and second filaments.

1. A power control device comprising a first and second electricaldischarge means in which said first means operates in the temperaturelimited region of a diode electrical characteristic and said secondmeans operates in a triode electrical characteristic and terminal meansfor applying power through said power control device to a load, saidfirst and second means of said device connected in electrical parallelto provide in combination an electrical characteristic corresponding toa substantially uniform power control electrical characteristic withvarying loads.
 2. The device of claim 1 in which said first means is anelectrical discharge control diode and said second means is anelectrical discharge triode.
 3. The device as set forth in claim 1 inwhich said first means is an electrical discharge control diode of highperveance and said second means is an electrical discharge control diodeof low perveance.
 4. The device as set forth in claim 3 in which saidfirst and second second means are within a common envelope and have acommon emitter.
 5. The device as set forth in claim 2 in which saidfirst and second means have a common emitter and a common anode.
 6. Thedevice as set forth in claim 1 in which said first means consists of afirst filament, said second means consists of a second filamentsurrounding said first filament with a bias provided between said firstand second filaments, and a common anode for said first and secondmeans.
 7. The device set forth in claim 6 in which said means forapplying power is connected to said anode and said load is connected tosaid first and second filaments.